Taurine (2-amino ethane sulfonic acid), an abundant but poorly understood amino acid, appears to have important actions in the heart on the movement of ions -- particularly potassium and calcium--and to be involved in the modulation of membrane function. The heart obtains taurine by two routes: endogenous biosynthesis and uptake from the serum. One part of this proposal is designed to elucidate in detail its biosynthesis and metabolism in the heart, and the other part is involved in a study of the regulation of uptake. Drugs that perturb taurine levels in the heart (such as isoproterenol, reserpine and thyroxin) will be given to rats and guinea pigs and the biochemical responses produced studied to obtain information on the regulatory mechanisms. The studies will be conducted on intact animals, perfused hearts, and cardiac subcellular organelles. The object of the study will be to define the biochemistry of taurine in the heart, understand the regulation of it, and integrate this knowledge with information on its pharmacological and physiological actions on the heart.